Impaired Systemic Oxygen Extraction at Maximum Exercise in Pulmonary Hypertension

PURPOSE: To determine the relative contributions of the Fick principle variables to impaired exercise tolerance in pulmonary arterial hypertension compared with pulmonary venous hypertension. METHODS: One hundred forty-seven consecutive, complete, clinically indicated cardiopulmonary exercise tests done with radial and pulmonary arterial catheters and radionuclide ventriculographic scanning were screened for an exercise limit attributable to 1) pulmonary arterial hypertension (N = 34), 2) left ventricular systolic (N = 23), or 3) diastolic dysfunction (N = 36), defined by mean pulmonary artery pressure, pulmonary capillary wedge pressure, and left ventricular ejection fraction. Systolic and diastolic dysfunction are together referred to as pulmonary venous hypertension. Patients with other limits were excluded, including those with a pulmonary mechanical limit. For the resulting 93 exercise tests, the Fick principle variables' contributions to a depressed maximum oxygen consumption were compared by ANOVA and ANCOVA. RESULTS: Maximum oxygen consumption (54.5 +/- 15.5 vs 73.2 +/- 20.1 vs 66.0 +/- 15.7% predicted) and oxygen delivery (1457 +/- 456 vs 2161 +/- 824 vs 2007 +/- 665 mL x min(-1)) were reduced in systolic dysfunction versus both diastolic dysfunction and pulmonary arterial hypertension, respectively (P < 0.05 by ANOVA). Maximum systemic oxygen extraction ratio was highest in systolic dysfunction, intermediate in diastolic dysfunction, and lowest in pulmonary arterial hypertension (0.744 +/- 0.091 vs 0.680 +/- 0.091 vs 0.619 +/- 0.113, respectively, P < 0.05 among all groups). Systemic oxygen extraction at peak exercise was inversely related to maximum cardiac output in pulmonary arterial hypertension, but it was blunted versus systolic dysfunction throughout the range of peak cardiac outputs (P < 0.05 by ANCOVA). CONCLUSIONS: Maximum systemic oxygen extraction is impaired in pulmonary arterial versus pulmonary venous hypertension and contributes to the exercise limit.